The invention relates to an electrically conductive resist material which can prevent electrostatic charging and the fields resulting therefrom, to a process for its preparation and its use, in particular for the preparation of electron beam resists.
It is known that in particular upon exposure to electron beams for producing very fine resist structures in the submicron region on non-conducting substrates such as glass, quartz, lithium niobate, undoped silicon, germanium or III-V semiconductors, electric fields are generated by means of secondary electrons, which deflect the primary beam, resulting in unsatisfactory image reproduction (cf. Appl. Phys. Lett. 48(13), 835 (1986)). Similar resolution-limiting effects are also observed in the use of scanning electron microscopy for inspecting and measuring integrated circuits.
Examples of suitable compounds for avoiding charging effects are as follows: indium oxide, tin oxide or ITO layers on glass substrates, to which the resist is then applied (cf. Chem. Abstr. 102, 229.567n).
The use of a carbon film as conductive bottom layer requires an additional heat treatment of up to 400.degree. C. after the deposition of the film. However, this may have the effect that subsequent or already performed process steps may become useless (cf. Appl. Phys. Lett. 48 (13), 835 (1986)).
By applying a solution of ammonium polystyrene sulfonate as top or bottom layer, it is also possible to suppress charging effects (cf. New Materials/Japan, 9 (5), 13 (1988)).
Furthermore, a resist material is known which comprises a conducting polymer tetracyanoquinone dimethane (TCNQ)salt complex in a PMMA matrix in order to avoid a charging effect. The disadvantage of this method is that TCNQ complexes are, as a rule, insoluble or slightly soluble, which may lead to phase separation when the resist material is applied. Moreover, TCNQ complexes are difficult to handle due to their toxicity and their decomposition at elevated temperatures(cf. Chem. Abstr. 108, 29440c).